It is said that HCFC-based refrigerant, such as R22, which is utilized in an air conditioner and is a stable compound, destroys the ozone layer. In recent years, HFC-based refrigerants are utilized as alternative refrigerants of HCFC, but these HFC-based refrigerants have the nature for facilitating global warming. Therefore, there is a tendency to start employing HC-based refrigerants which do not destroy the ozone layer or largely affect global warming. However, since the HC-based refrigerants are flammable, it is necessary to prevent explosion or ignition so as to ensure safety, and it is required to reduce the amount of use of the refrigerant to the utmost. On the other hand, HC-based refrigerants do not have lubricity and are prone to be solved into lubricants. Therefore, when HC-based refrigerants are used, the use of an oil free or oil poor compressor is required, and a linear compressor in which little load is applied in a direction perpendicular to an axis of a piston.
Here, a linear compressor in which a linear motor is disposed around an outer periphery of a piston is disclosed in Japanese Patent Application Laid-open No. H8-144954, Japanese Patent Application Laid-open No.H4-34760 and U.S. Pat. No. 5,525,845.
However, in the above prior art, there is no suggestion to easily mount a movable member of a linear motor to a piston with high precision.
It is described in Japanese Patent Application Laid-open No.H4-34760 that a piston is provided at its end with a flange, and the flange is concentrically provided with a cylindrical bobbin. However, there is no description as to how the bobbin is provided concentrically. Further, as shown in FIG. 1, of the publication the flange is provided merely for mounting the bobbin by a screw. Therefore, the mounting precision of the bobbin to the piston can not be enhanced by this prior art.
Therefore, it is an object of the present invention to provide a linear compressor in which it is possible to easily mount a movable member of a linear motor to a piston with high precision.
Further, when the movable member is a permanent magnet, it is another object of the invention to provide a linear compressor in which it is possible to easily mount this permanent magnet with high precision.